Dicranum drummondii, primarily an Eurasian species, was for years confused with the endemic North American species Dicranum ontariense W. L. Peterson (see discussion under 9. D. ontariense). It was only recently (August 2000) that W. B. Schofield, S. S. Talbot, and S. L. Talbot made the first and only collection of the species, which was sterile, from Attu Island in the Aleutian Islands. The species is best recognized by its robust size, stems 5-11 cm, its leaves yellowish green to yellowish brown, undulate or rugose, erect and compressed, becoming flexuose at the tips when dry, concave below and keeled above, with an oblong-ovate base, becoming long-acuminate at apex, margins strongly toothed above, and costa percurrent to shortly excurrent, without lamellae. Microscopically, distinguishing characters are the leaves in the distal part with round, oblong, somewhat rectangular cells with few pits, cells smooth or prorate on abaxial surface, in cross section the lamina with a few scattered 2-stratose cells, cells walls between the lamina cells not bulging, and costa with a few cells differentiated on the adaxial epidermal surface.